1. Field of the Invention
The invention relates generally to a backlight and more particularly to backlights including lightguides formed with optical structures in one or more surfaces of the lightguide.
2. Description of the Related Technology
Backlit display devices, such as liquid crystal display (LCD) devices, commonly use a wedge-shaped lightguide. The wedge-shaped lightguide couples light from a substantially linear source, such as a cold cathode fluorescent lamp (CCFL), to a substantially planar output. The planar output is then used to illuminate the LCD.
One measure of the performance of the backlit display is its uniformity. A user can easily perceive relatively small differences in brightness of a display from one area of the display to the next. Even relatively small non-uniformities can be very annoying to a user of the display.
Surface diffusers or bulk diffuser sheets, which scatter the light exiting the lightguide, are sometimes used to mask or soften non-uniformities. However, this diffusion also results in light being directed away from a preferred viewing axis. A net result can be a reduction in overall brightness of the display along the preferred viewing axis, which is another performance measure of a display device.
From a subjective standpoint relatively small increases or decreases in overall brightness are not as easily perceived by the user of the display device as are discrete nonuniformities. However, the display device designer is discouraged by even the smallest decreases in overall brightness including decreases so small they might only be perceived by objective measurement. This is because display brightness and power requirements of the display are closely related. If overall brightness can be increased without increasing the required power, the designer can actually allocate less power to the display device, yet still achieve an acceptable level of brightness. For battery powered portable devices, this translates to longer running times.